DE2807397A1 - FLOW MEASURING DEVICE FOR A FLOW MEANS - Google Patents

Description

PATENTANWÄLTE A. ß. \

DIPL-

H. KINKELDEY

DR-ING

W. STOCKMAIR

CR-ING · A »E ICALTECH

K. SCHUMANN

DR RER .MAT. ■ DIPL-PMYS.

P. H. JAKOB

P 12 406 G. BEZOLD

The Perkiri Bucket Corporation

8 MUNICH EOrWalk, Connecticut 06856 Maximilianstrasse

Main avenue

February 21, 1978

Flow meter for a fluid

The invention relates generally to the field of Flow meters and in particular acoustic flow meters for measuring the flow rate of a fluid along an enclosed path.

A typical flow meter using acoustic waves is described in US Pat. No. 5,109,112. This Flow meter has a pair of transducers for generating and receiving pressure waves in either audible or audible mode Ultrasonic frequency range. These converters are arranged within a housing through which the fluid flows. The transducers are alternately in the transmit and receive mode, so that pressure waves through the transmitting transducer are generated in the gas and are received by the other transducer. By measuring the The phase difference between the transmitted and received waves in both directions is the speed of the determined by the transducer passing gas.

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2607397

A modification of that in the aforementioned US patent flow measuring device described is based on converters, which have a transmitting and a receiving part are equipped to deal with any problems resulting from changes in the gas composition or temperature of the To exclude gas essentially.

The above known apparatus requires that the converter be placed in the flow path of the gas whose speed is to be measured, or is arranged in a cavity in the pipe wall. In either arrangement, the normal flow of fluid will be changed significantly as it flows past the converter, thereby reducing the accuracy of the flowmeter. rätes suffers. In addition, solid particles can or the like in the fluid. gather around the converters, whereby the transmission and reception properties of the transducers are impaired.

In an attempt to overcome these and other difficulties in the known acoustic flow meters, a flow meter has been developed which has no obstacles along the flow path and is disclosed in U.S. Patent Application Ser. 599 24-5 described by the 24-.JuIi 1975 which corresponds to the US-PS 003 252 M-. In this flow meter, the transducers are generally cylindrical in shape and are located within the turn of the flow conduit, thereby eliminating any indentations in the flow path as well as voids in the conduit wall in which debris could collect.

Although this flow meter has obstacles in the flow path of the fluid as well as voids in the conduit wall eliminated, it may ground inaccurately or completely

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fall when the composition of the flowing through it Gas is different from that for which the flow meter is calibrated. Indeed this is a common problem with most acoustic flow meters because of the speed of the acoustic Pressure within a gas is a function of its chemical composition, so the accuracy of typical acoustic flow meters depends on its balance for the particular gas its flow to measure is. The need to readjust each time when the flow meter is to be used for a different gas, it is at least inconvenient at best. In applications where the gas composition changes changes during use of the flow measuring device, e.g. in pulmonary activity puncture analyzers, are acoustic Flow meters inaccurate unless corrective feedback is provided from a gas analyzer to compensate for a change in the gas composition.

It is therefore an object of the invention to provide a flow meter which is independent of changes in gas composition or the temperature is accurate during "its use.

It is another object of the invention to provide a flow meter to provide a device for automatically adjusting the operation of the flow meter as a puncture of the dynamic changes in gas composition and gas temperature and effect a measurement of the speed of sound which is itself on average Molecular weight of the gas is based.

The invention comprises an acoustic flow meter which, in its preferred embodiment, has two in one Wall of a line arranged converter, so that no

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There are obstacles to the flow of gas and no voids in the wall that provide a place for the collection of particulate matter Would represent material. The converters are connected to an electronic circuit, which alternates one of them switches to transmit mode and the others to receive mode. An automatic shift adjuster is provided to set the transmission frequency so that the energy generated by the transmitting transducer acoustic pressures on a receiving transducer is maximum in order to allow speed changes of the acoustic Compensate for pressures in the gas caused by changes in gas composition or temperature.

The electronic circuit has a circuit arrangement for measuring and storing the phase difference between the Signal to the transducer sending the acoustic pressures and that of the receiving transducer based on the acoustic Depress generated signal during each of two consecutive transmit-receive cycles. A circuit device is intended to determine the difference between two successive phase differences, of which at least one previously stored, the sign being the difference between the direction of gas flow and the magnitude of the Difference correspond to the speed of the gas flow through the flow meter. Circuits are also for Form the sum of two successive phase differences provided which are proportional to the speed of sound in which they move through the flow meter Are gas.

According to a preferred concept of the invention, there is thus a flow measuring device for the precise determination of the flow velocity A gas is essentially independent of its molecular composition and also for determination a measurement of the speed of sound in the gas is created.

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The gas flows through a converter assembly. In the converter two cylindrical transducers are provided that each generate acoustic pressures or can respond to these in the gas. The converters are alternating between the send and receive mode switched over, so that at a given moment the one to send and the others are used for receiving. The phase difference between the transmitted and received signals are stored for two consecutive transmit-receive cycles, where the difference between two successively stored phase differences is the size and the Indicating the direction of fluid flow and the sum the stored phase differences a measure of the speed of sound in the gas indicates. The flow meter has a circuit for automatically compensating for Changes in the gas composition so that the specified Flow rate is correct at all times.

An embodiment of the invention is explained in more detail with reference to the drawing. It shows:

Fig. 1 is a schematic representation of the flow measuring device, including a converter arrangement, and a block diagram of the circuit assigned to it,

Pig. 2 shows a detailed circuit of a timing pulse generator for controlling the operation of the circuit shown in FIGS. 4 and 4,

FIG. 3 shows a time-pulse diagram for the circuit of FIG and

Figs. 4-6 show detailed circuits of an embodiment the flow measuring device according to the invention, which the time pulses generated by the circuit of FIG. 2 are used.

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As shown in Fig. 1, the inventive Flow meter on a transducer assembly 10, which in Longitudinal section is shown, has a substantially cylindrical body with a central bore which extends through assembly 10 and through which gas flows in a direction indicated by arrows 12. These arrows 12 indicate the gas flow through the converter arrangement 10 in a view from left to right in FIG 3? Ig. 1 at. However, gas can flow through the assembly 10 in the opposite direction if so desired is.

The converter arrangement 10 is designed essentially in accordance with the description in U3-PS 4 003 252, the disclosure of which is hereby incorporated into the description. Thus, the transducer assembly 10 of the present invention may additionally include a cylindrical housing made of metal or other suitable material, shown in ^{FIG. 5 1 Xg.} 1, not shown, which surrounds the support member 14. The support member 14 itself is preferably made of polyurethane foam, foam rubber or some other material that has good acoustic damping properties. Two annular recesses 16 and 18 are formed in the interior of the support member 14 and are spaced from one another along the path of the fluid flow indicated by the arrows. Two additional circular recesses 14 and 22 are arranged at the opposite ends of the support member 14.

Each within and in contact with the surfaces that form each annular recess 16 and 18 is a cylindrical transducers 24 and 26, each of which has an inner cylindrical bore passing through it and being substantially uniform with the inner ones cylindrical bores 28 extending between the annular recesses of the support member 14.

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Converters with a different geometry, such as domed converters, can also be modified with appropriate modifications the remaining parts of the transducer assembly 10 are used to drill a centrally located bore therethrough, with no obstacles and no voids in the bore wall to obtain a collection point for particulate matter would be.

Within each circular recess 20 and 22, an end ring 30 and 32 is respectively arranged, which is preferably made of a sound-absorbing material, such as a polyurethane damping foam, similar to the Y-370 vibration damping tape, manufactured by 3M Corporation. Materials that are similar sound-absorbing Properties can also be used for the end rings 30 and 32 can be used. The end rings 30 and 32 each have a cylindrical inner bore which is substantially flush with the adjacent cylinder bores 28 of the Support member 14 extend. The flow path through the transducer assembly 10, as indicated by the arrows 12, therefore has an essentially continuous wall so that the fluid flowing through it does not pass through any Projections or cavities is obstructed.

The converters 24 and 26 can be any of a number of conventional ones Have bodies arranged in radial or hoop-shaped Working manner to create acoustic pressures within the gas flowing through the assembly 10. Examples of suitable materials for transducers 24 and 26 include cylindrical bodies made from Polyvinyl fluorides or other high polymer organic, Piezoelectric materials are made, ceramic converters made from barium titanate, lead oxide titanate or other polarized, polycrystalline, ferroelectric, ceramic materials, quartz, tourmaline, or equivalent

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electromechanical ^ arrangements include those skilled in the art are known.

The inner and outer surfaces of transducers 24 and 26 have conductive coatings on them that provide electrical Form feed electrodes. The conductive coatings on the inner surfaces of transducers 24 and 26 are over, respectively Lines 34 and 36 with externally arranged crystal drivers / Receiver circuits 38 and 4-0 connected. The conductive coatings On the outer surface of transducers 24- and 26 are via lines 4-2 and 4-4, respectively, to the crystal driver / receiver circuits 38 and 4-0 connected. The electrical connection extender pairs 34-, 4-2 and 36, 44- for the transducers 24 and 26 each pass through openings 4-6 and 4-8, each from the outside of the arrangement 10 are connected to the converters within the annular recesses 16 and 18. The mode of operation of the converter arrangement 10 in connection with the electronic circuit is basically the same as in the aforementioned US-PS 4,003,252 is described so that its disclosure also, in this regard, is included here. Basically. however, the "transducer assembly is via a flexible sheath, tube or the like with an external source of fluid connected, the flow rate of which is to be determined. The fluid itself can be either a gas or have a liquid, although the illustrated embodiment of the invention is particularly for measuring the gas flow is designed when it flows through the transducer assembly 10 in an axial direction that passes through the Arrows 12 is indicated, or in the opposite direction. A control circuit 50 is in each case via lines 52 and 5 ^ Eiit the converter-driver / receiver circuits 38 and 4-0 connected. The control circuit 50 causes one

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the converter driver / receiver circuits 38 or 40 for sending an electrical signal to the respective cylindrical converter 24 or 26 connected to it, Honoring the other driver / receiver circuit 40 or 38 receives a signal from the transducer 26 or 24 connected to it. As previously stated, the converters speak 24 or 26, which receive electrical signals from a driver / receiver circuit, act on them by generating them an acoustic pressure in the fluid. At the same time, the other is talking to the other driver / receiver circuit 38 or 40 connected transducers to the acoustic pressures in the fluid by generating an electrical Signal that is detected by the driver / receiver circuit connected to it.

The acoustic pressures generated at one of the transducers 24 or 26 require a finite time to separate from the transmitting Transducer to propagate to the receiving transducer with the propagation time determined by the sighting and the speed the fluid flow through the transducer assembly 10 and the speed of sound in the fluid flow within the arrangement 10 depends. These relationships are detailed in the aforementioned U.S. patent described.

As an alternative to the converters previously described, each converter 24 and 26 can be replaced by a pair of converters be, which are arranged in the arrangement 10 in the same V / eise. Of the pair of converters, one is special one for transmitting, i.e. generating acoustic pressures, and the other for receiving, i.e. generating an electrical one Signal is formed as a function of acoustic pressures in the gas.

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The converter assembly 10 and the circuitry connected to it work in the following way. The control circuit 50 first causes one of the converters, either the converters 24- or 26, creates acoustic pressures in the fluid, and at the same time that the other transducer, either 26 or 24, which receives acoustic pressures from the first transducer. This mode of operation is a first send-receive cycle. A transmission signal is simultaneously received from the control circuit 50 via one of the lines 52 or 5 ^ to a driver / receiver circuit 38 or 4-0 and via line 56 to a phase detector 58 given. A received signal from the receiving one Converter 24 or 26 is connected to one of the converter driver / receiver circuits 38 or 40 via lines 60 or 62 are given to the phase detector 58, respectively. Of the Phase detector 58 responds to the transmit signal and the received one Signal by generating a signal on the line 64- that the phase difference between the transmitted and the received signal. This information is added to a phase via line 64-? and subtractors 66 given, which is a memory device for temporarily storing the phase difference received from the phase detector 58 having.

The control circuit 50 then reverses the Rolling the converter 24- and 26. That means, the other converter 24- or 26 is switched to its transmission mode, to generate acoustic pressures in the fluid, and the first transducer 24 or 26 is switched to its receiving mode. This way of working forms a second Send-receive cycle. The phase detector 58 operates during of the second transmit-receive cycle to determine the phase difference between the transmitted signal and the received signal and this second phase difference is via the line 54- to the phase adder and subtractor 66 given, which also temporarily stores this second phase difference.

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The phase adder and subtracter 66, after both phase differences are stored in it, calculates both a sum and a difference between the two stored phase differences. The difference between the two stored phase differences with a further correction made in connection with I ¹ Xg. 6, is indicated on the output section 68, which, when the flow measuring device according to the invention is calibrated, indicates the flow rate through the converter arrangement IO. In addition, the sign of the difference between the two phase differences, which are calculated by the phase detector 58, indicates the direction of flow through the converter arrangement 10, with a positive sign an arbitrarily selected direction of the fluid flow through the arrangement 10 and a negative sign the opposite direction of the fluid flow indicate.

The sum of the two phase differences as shown by the Phase adder and subtracter 66 is calculated is indicated on output line 70. The size of the signal on line 70 is proportional to the speed of sound in the gas flowing through assembly 10, compared to the speed of sound in the reference gas used for the adjustment. The total is also about the line 72 transmitted to the control circuit 50, the so that it is used in a manner to be described in detail later. In addition, it is used to correct the flow rate used on line 68. The value given on the output 70 is a relative value and the flow meter according to the invention must be calibrated in such a way that the magnitude of the value on line 70 is interpreted can be.

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⁰ XH

As generally indicated above, failure of the flow meter described in the aforementioned US Pat. No. 4,003,252 is due to the flow meter failing to operate in ambient conditions where the speed of sound in the gas passing through the transducers during its operation Usage changes dynamically. The cylindrical transducer system has been found to operate by building up a strong resonance echo across the diameter of the tube at one or more natural frequencies. For example, the relationship can be approximately 2.3 λ = D, where χ is the wavelength of the sound in the fluid in centimeters and D is the inner diameter of the crystal and the tube in centimeters. The frequency at which the resonance echo occurs above diameter D is called the natural cavity resonance frequency of the O2 mode. Other useful frequencies at which resonance echoes occur are those at which D is substantially equal to 0.73>, 1.4-λ, 3.2> or 3.9 λ. The reason for the previously described failure of the flow meter is then due to the fact that the velocity of the acoustic pressures within the gas flowing through the transducers changes as a function of the gas composition. This causes the amplitude of the acoustic pressures sensed by the transducer of the arrangement, which is in receiving mode, to change because the inside diameter of the transducers is no longer equal to the natural wavelength, thereby increasing the size of the generated by the receiving transducer Signal drops sharply- Therefore, it becomes more difficult to detect the received signal, which creates the possibility of detection errors or a complete failure in detecting acoustic pressure. This failure can be eliminated by changing the inside diameter dimensions of the transducers within the assembly or by changing the frequency of the acoustic pressures generated by the transmitting transducer. Since the

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Shaper arrangement itself for setting the inside diameter the converter is not suitable, it is of course better to solve this problem by adjusting the frequency of the acoustic pressures generated by the transmitting transducer. The sum of the phase differences, as calculated by the phase adder and subtracter 66 is therefore sent via line 72 to the Control circuit 50 given. As previously indicated, the signal on line 72 is related to the switching speed in the gas flowing through the assembly 10. This signal is from the control circuit 50 to Change the frequency of the acoustic pressures used by the transmitting transducer during each transmit-receive cycle are generated in order to keep the wavelength constant and the signal picked up by the receiving transducer to make it as big as possible.

It was also found that after correcting the frequency To keep the wavelength constant, the occurring flow velocity is multiplied by the speed of sound must be in order to obtain an accurate flow rate measurement regardless of the change in gas composition to create. Experiments have shown that flow meters of the type described in the aforementioned US patent Type sometimes subject to errors as a result of ejection of acoustic pressures from other parts of the system, by connecting the transducers «These reflections often result from the acoustic pressures, that ricochet off other fluid transfer ports connected to the transducer assembly. Problems have also arisen when the converter itself is used in breathing air analyzers, where it is more densely packed Physically arranged in the vicinity of the mouth of the individual whose breathing air is to be analyzed.

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The present invention overcomes the reflection problem. by. Providing the end rings 30 and 32, which are attached to each other opposite ends of the arrangement 13 are arranged. These rings 30 and 32 are made of an acoustic damping material, like the aforementioned material, which significantly reduces the amplitude of the acoustic pressures caused by them go through. In fact, the amount of damping they provide is if a suitable material for the hinge 30 and 32 is chosen, sufficient so that ^ an end of the Arrangement 10 can be arranged in the immediate vicinity of the mouth of an individual whose breathing air au analyze and that of other acoustic flow meters Problems arising as a result of acoustic reflections are thus essentially eliminated. The through the Rings 30 and 32 essentially eliminate damping also the problems with reflections when the assembly 10 is coupled into the fluid carrying systems.

The above explanation in connection with 5 ¹ Ig. 1 has generally described the circuit and operation of the invention. The circuits of Figs. 2 and 4-6 show actual application of the invention in connection with a breathing air tester, but those skilled in the art will readily appreciate that other circuits can be used and that the components can be changed to make the circuit to optimize for use in other applications for the invention.

The circuit of FIG. 2 has a pulse generator for generating control pulses to the in FIGS. 4- to 6 to operate the circuits shown. Fig. 3, on the other hand, shows a timing diagram showing the pulse train for different Shows output signals of the circuit of FIG. The circuit of Figure 2 includes an integrator circuit

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01) 4047 on, with the a. 121X resistor and a 4700PF capacitor is connected to control the output frequency, which is 4-00 KHz for the mentioned resistor and capacitor. Two J.-K flip-flops connected in series, each representing one half of an integrated circuit CD4027, are used to generate timing pulses whose speed is slower than that generated by the oscillator formed from the integrated circuit CD4047. The signals generated by the oscillator and the flip-flops are passed through TJIiD and HAIID gates of the Pig. 2 are combined to generate pulse trains as shown in FIG. 3, respectively. A pulse diagram for the output Q ₀ is not shown in Fig. 3, but it carries a pike-wave signal with a frequency that is twice as large as for Q ^ l, and a positive leading edge of a pulse on the line labeled Qq occurs at the same time as the positive leading edge of a pulse at the output Q ^ of the circuit CD4047

As shown in Fig. 5, constitutes an integrated circuit CD4046 a · voltage controlled oscillator (VCO), which a Square-wave signal generated at output 4, the frequency of which is determined by the resistors in series between the terminal 11 and earth are connected, as well as by the voltage applied to terminal 9. For the particular ones shown in Fig. 5 shown resistors and a voltage of about +7 »5 volts at terminal 9 is the frequency of the square wave signal at the output 4 of the voltage-controlled oscillator nominally 51 KHz A change in the voltage appearing at input 9 causes a shift in the frequency of the voltage controlled oscillator. The circuit shown in Fig. 5 causes one dynamic change in the frequency of the VCO as a function of changes in the speed of sound in the gas in a described in more detail later.

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The square wave signal from the voltage controlled oscillator at connection 4 reaches connection 3 of the circuit GD4046 via a line 100, which internally has a phase detector (0DST) forms. The square-wave signal also reaches a HAKD element via a line 102, the output of which is connected to an operational amplifier LM318 and an XR2208 operation multiplier connected is. The function of these circuits is to produce a sinusoidal signal on terminal 104 that is the same Frequency like the square wave signal appearing on line 102. However, those skilled in the art will immediately recognize that the Circuit between line 102 and terminal 104-just one circuit of many known circuits for reshaping a square wave signal into a sinusoidal signal, so that other equivalent circuits can also be used.

Between the connection 104 and the output connection AG, three are formed from the circuit types LN318 and 804-3C Operational amplifier provided. The operational amplifier LM318 amplifies the sinusoidal signal at terminal 104 ·. The two Operational amplifiers 8043C set the phase of the signal that appears at the output at the end AC, with one te llxd.de resistances 106 and 108, with which the phase of the signal at the output terminal AG can be adjusted by about 360 ° can . These resistances are set during the calibration of the flow measuring device and are preferably grounded in this way set that the signal at terminal 9 of the circuit CD4046 is +7.5 volts, with no air through the transducer assembly 10 (Fig. 1) flows. The following description describes the mechanism by which the phase adjustment of the signal at the output terminal AC causes a change in the voltage at the terminal 9.

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The circuit shown in Fig. 4- shows converter-driver / Receiver circuits and shows how these are connected to converters 24 and 26. The circuit of the Pig. 4-is divided into a driver part, shown to the left of the dashed line 110, and a receiver part, which is shown to the right of dashed line 110 but does not include transducers 24 and 26.

The sinusoidal signal from the circuit of FIG. 5 is applied to the Input terminal 'AC in Pig · 4- and then on two converter-driver circuits given, the first driver circuit including Q5 and the second driver circuit Q6. These transistors Q5 and Q6 combine the sinusoidal signal from the input terminal AC to the respective connected converter 24 or 26, whereby these get into their transmission mode. 'The Link signals are from transistor pairs Q1, Q3 and Q2, Q4 and the respective connected circuits are generated, which is the circuit of the Pig. 2 to generate the logic signals that are applied to the terminals X and T appear. Since the logic signals at the connections X and Y occur at different times and themselves alternate, like this one in Pig. 3 is shown, the converters 24 · and 26 are alternately switched to their transmission mode.

Receiver circuits 116 and 118 are also directly connected to transducers 24- and 26, respectively, but receiver circuits 116 and 118 are either active or inactive to respond to signals generated by transducers 24- or 26 connected to them , depending on whether the short-circuiting transistor % / or Q8 connected to them is conductive or blocked. The transistor Q7 is z.3. through a

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Linking pulse signal Q3 controlled and connects the Line 112 to ground when signal Q3 is positive. Likewise, transistor Q8 connects the line 114 with earth if the link signal ζ £ positive is. From the timing diagram of FIG. 3 it can be seen that that Q ^ is always positive when X is positive, so that the receiver 116 is thus ineffective when the converter 24 is in its transmission mode and Receives signals from the input terminal AC. In the same Thus, the receiver 118 is ineffective whenever QT is positive when the transducer 26 is in the transmit mode, if therefore a given converter 24 or 26 is in the transmission mode, so that is with them connected receiver circuit 116 or 118 ineffective. However, if one of the converters is in transmission mode, the one connected to the other converter is 24 or 26 Receiver circuit 116 or 118 effective, since the associated "logic signal Q- or q7 shows ground potential. So is located e.g. during a first send-receive cycle the converter 24- is transmitting and holding signals from the input terminal AC, transistor Q7 is conductive by signal Q ^ to receiver 116 by ground line 112 turn off, and the receiver circuit 118 is operatively connected to the converter 26, as the transistor Q8 as a result of the link signal that is at ground potential (JT is conductive. At the same time, the Linking signal T at ground potential, which prevents the signal appearing at the input connection AC from being transmitted transistor Q6 can pass to converter 26. The second transmit-receive cycle occurs when the converter 26 receives signals from the input terminal AC, the transistor Q7 is blocked by Q ^, the transistor Q8 by JT is switched on, the logic signal T is positive and the logic signal X is on earth

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potential is. Therefore, the uniform is 26 in transmission mode, the receiver 116 is effective and the receiver 118 is ineffective.

The receiver circuit 116 connected to the converter 24 has two operational amplifiers 120 and 122, which are shown in FIG Are connected in series and are always effective when the transistor Q7 is not conductive to any of the Input line 112 appearing signal to amplify. The amplified signal appears at connection 6 of the operational amplifier 122, the one with the inverting input of a compares r circuit 12A- is connected. The comparator circuit 124- is always effective when the link signal A is at a logic level of 0, which allows the output signal to appear on terminal 7. The output signal at terminal 7 there is a positive voltage of about +15 volts when the sine input signal is at terminal of comparator circuit 124 · has a negative potential, and is 0 volts when the input signal is at the terminal 3 has a positive potential. The comparator circuit therefore forms the sine input signal into a square output signal around. The comparator circuit 126 connected to this is for the duration of the effectiveness of the comparator circuit 124 ineffective and vice versa.

The receiver 118 has two operational amplifiers connected in series 130 and 132 on the that on the singing line 114 appearing signal and this amplified signal to the output 6 of the operational amplifier 132 give. This output signal at terminal 6 of amplifier 132 is applied to the inverting input of the comparator circuit 126 given, which is always effective when the link signal B is at a logic level -vgq 0. The output signal at connection 7 of the comparator

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section 126 is a right designal with a tension of about +15 "volts, if there is always an input signal at the connector 3 has negative potential, and of about 0 volts whenever the input signal at terminal 3 is positive Has potential. Since the linking signals A and B are different Times appear does not affect the operation of the comparator circuit 12A or 126 the operation of the other comparator circuit 126 or 124.

The comparator circuits 124 and 126 are therefore independent effective from each other to generate square-wave signals at their respective outputs from the sinusoidal signals that at the converters 24 or 26 connected to them are always generated when the "converter is in the Receive mode is located and the required link signals are present to operate the receiver circuits 116 or 118. As the output terminals of the comparator circuits are interconnected at the connection SIG, the signal appearing at the connection SIG gives the logical TJITD link at the comparator outputs 124 and 126 appearing signals.

The output signal from the receiver circuits 116 and 116 is applied to the terminal labeled SIG in FIG the associated input terminal designated by SIG in FIG. 5 and then applied to the terminal 14 of the integrated circuit CD4046, which is internally connected to the Phase detector circuit is connected. The phase detector itself works just like an EXCLUSIVE-OR circuit, whose output is internally connected to a terminal 2 of the integrated circuit CD4046 and a Output level of a logical 1 always has when only one input of the phase detector has a level with a

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logical 1 receives. The one at terminal 2 of the integrated circuit CD404-6 appearing signal is therefore a square wave signal, which is pulse width modulated, the width of each pulse being based on the phase difference between the transmitted one Signal, i.e. the signal on line 100, and the received signal, i.e. that at terminal 14 of the integrated Circuit CD4046 appearing signal.

In the normal operation of the flow meter according to the invention, when the composition of the gas flowing through the transducer assembly 10 changes from that in which the flow meter was adjusted, the Pnase of the SIG at the input is in S ¹ Xg. 5 is different from the signal phase that appears at this input terminal when the circuit has been balanced. The output of the phase detector is therefore different, whereby the voltage across the 1 MP capacitor of a low pass filter, which comprises a 1 MO resistor and an IMF capacitor and is connected to the output of the operational amplifier 156, changes from the voltage at which the flow meter has been trimmed in a manner which will be described in detail later. This change in voltage across the IMF capacitor causes the voltage at terminal 9 of the integrated circuit GD4046 to change, whereby the frequency of the signal generated by the voltage-controlled oscillator also changes. The system continues to adjust the frequency of the voltage controlled oscillator until the phase difference between the transmitted and received signals no longer causes a voltage change across the 1MF capacitor in the low pass filter.

The possibility of changing the working frequency depending on a change in the gas composition is available in the Particularly important with regard to the present invention,

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since the previous systems cannot do this. It can be shown be that the converter according to the invention has a maximum Effect energy transfer from the transmitting to the receiving transducer when operated at their natural frequency which depends on the inner diameter of the converter. Therefore, if air is the gas in the converter assembly the flow meter is adjusted, the frequency of the voltage controlled oscillator corresponds to that, the generate acoustic pressures with a fraction of half the wavelengths across the transducer diameter in air, which corresponds to a natural frequency. If the gas density changes afterwards, the speed of the sound pressures also changes in this, whereby a different phase difference is detected by the nose detector. This causes a change in the frequency of the acoustic pressures produced by the voltage controlled oscillator, in a manner to be described later, and it can be shown that the new frequency corresponds to one at which the diameter of each transducer again corresponds to the number of eigenvalues of half the wavelength at the new frequency for the gas then located in the converter arrangement. In this way, a maximum energy transfer between a sending and a receiving transducer is achieved keep up.

The pulse-width-modulated signal that appears at the output of the phase detector is one "^ n two input signals for a UKD element 140, the output of which with a Integrator circuit 142 is connected. The second input of the UHD element 140 receives an integration enabling Signal IE, which is a logical 1 whenever either the link signal A or the link signal B is a logic 0, which is a condition indicating that the output of the phase detector is the Phase difference between an emitted and a received signal. That way it becomes

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pulse width modulated signal supplied via the UÜD element 1W, xvenn it through, the signal that enables integration IE is conductive. The output of the integrator circuit 142 appears at output 6 of the operational amplifier LM318 and has an integrated level during the duration of the integration enabling signal, its final level to the phase difference between the transmitted signal from one transducer and the received signal from the other Converter is assigned and via a line 144 to an input terminal 5 of two different scanning and holding circuits 146 and 148 is given. Each sampling and hold circuit 146 or 148 samples the terminal 5 appearing voltage when a "logic signal to each of the respective control inputs at the" logic connection 6 is given. The sampled voltage appears at terminal 11 and has the same level as it is at terminal 5 appears when the link signal was present. the Voltage at terminal 11 of each sample and hold circuit 146 or 148 remains between logic pulses unchanged at connection 6. The sample and hold circuit 146 is always activated for its sampling operation when the signal appearing at the input terminal U is a logical 1. Similarly, the sample and hold circuit 148 is always driven into its scanning mode when the input terminal D carries a logical 1.

Between the sampling operation, either the sampling and holding circuits 146 or 148, an integrator reset signal appears at the input terminal IE, which a transistor Q12 turns conductive to a capacitor between the terminal 6 and the terminal 2 of the operational amplifier within the integrator circuit 142 to short-circuit. This resets the integrator so that its output voltage is the same O XEt.

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The sample and hold circuits are active during operation 146 and 148 are effective to store DC voltages that the phase difference between the transmitted signal at one transducer and the received signal at the other Specify converter. In the case of the sample and hold circuit 146, which is controlled by a drive signal at the input terminal U is controlled, a voltage is stored that is determined by any definition of the phase difference between the signal sent by the downstream converter 26 and the signal sent therefrom at the upstream lying converter 24 corresponds to the generated signal, namely a so-called upstream phase difference. On the other hand is the sample and hold circuit 148 is effective as a function of a drive signal D in order to store a voltage, this corresponds to the phase difference between the signal transmitted by the downstream converter 24- and the signal depending on the signal generated by the downstream converter 26, namely the so-called downstream phase difference.

The output from the sample and hold circuits 146 and 148 is applied to the inverting and the non-inverting, respectively Input of an operational amplifier 150 given, the one voltage at its exit at terminal 14 which is equal to the difference between the voltage applied to its non-inverting input terminal and the voltage appearing on its inverting input terminal is (0ΐ) -0ΐΓ). As stated earlier, this difference gives the uncorrected flow rate of a gas through the converter arrangement 10 (3? ig.i) at. In order to properly balance the flow meter, the non-inverting input terminal of the operational amplifier has a single digit marked 152 tzwerk, which is connected to it, in order to adjust the voltage on the non-inverting singing terminal so that

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the voltage appearing at the output at connection 14- is always equal to D when the flow rate through the converter arrangement ΛΟ is equal to 0. This adjustment circuit 152 compensates for various circuit alignment errors, particularly those of the sample and hold circuits 14-6 and 14-8.

The output signal from the sample and hold circuits 14-6 and 14-8 xdürd each via a 20 K -V / resistance to the input terminal .5 of a further A ^ sample and hold circuit 154-given. Since the output signals of the sample and hold circuits 146 and 14-8 are passed in the manner shown, the voltage at terminal 5 of the sample and hold circuit 154- is half the sum of the two-phase differences, which are stored in the two sample and hold circuits 14-6 and 14-8. This sum is within the Sample and hold circuit 154- depending on one Summing signal stored at the input terminal 5 is obtained. The output signal of the sample and hold circuit 154- is via a further operational amplifier 156 passed on, which generates a DC voltage at output terminal 8, which is related to the sum of the phase differences, those in sample and hold circuits 14-6 and 14-8 to the Time are stored when the control signal appears «As already stated above, this voltage occurring at the output terminal 8 of the amplifier 156 has ((2fD + 0U) a relative specification for the shell speed in the Gas within the converter assembly 10 on.

The one appearing at terminal 8 of amplifier 156 Voltage (0D + 0U) is fed back to a low-pass filter, one iMß resistor and one IIIF capacitor having. The voltage appearing on this IMF capacitor is given to a terminal 9 of the circuit GD4O4-6, the internally with the voltage controlled oscillator

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is connected and thus adjusts its operating frequency. The frequency of the voltage controlled oscillator therefore becomes with a change in the speed of sound in the gas changed within the converter assembly 10.

The circuits of Figures 4 and 5 in conjunction with the circuits the gig. 2 generate a signal at the output terminal 14 of amplifier 150 that of uncorrected flow by the converter arrangement 10 corresponds, and a further output signal at terminal 8 of the "amplifier 156, which the The speed of sound in the gas within the converter assembly 10 corresponds. iTaccording to the sails in determining of converter 24 as an upstream converter and of converter 26 as a downstream converter whenever the output 14 of the amplifier 150 appears Voltage is negative, that negative voltage that the fluid is actually in through the transducer assembly a sifting from the upstream converter 24 to the downstream converter 26 flows. In addition, the Size of the appearing at terminal 14 of amplifier 150 Voltage related to the circuit shown in Fig. 6 and corrected by this to the flow rate of the fluid passing through the arrangement 10. On the other hand, is the voltage at the terminal of booster 150 is positive, it indicates that the fluid is being sifted through assembly 10 flows from the downstream converter 26 to the upstream converter 24. Again, the size corresponds to the voltage appearing at terminal 14 of amplifier 150 the uncorrected flow rate through the converter assembly 10.

In the circuit shown in Fig. 5, however, the output signal is of amplifier 156 only one to the speed of sound in the gas related information. In order to

, 809838/0601

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determine whether the speed is greater or less than is the one for which the flowmeter was calibrated, the amplitude at the time of calibration must be recorded and then compared to the current reading. However, the circuit can be modified in a simple manner that the output voltage is zero whenever the balancing fluid is in the transducer assembly is available. If the speed of sound then changes in the fluid, the output voltage is decayed positive or negative and the sign of the voltage corresponds to the difference from the speed of sound compared has increased or decreased in the fluid that the flowmeter was being balanced. The size of the output voltage then corresponds to the relative one Difference between the speed of sound in the gas that instantly passes through the transducers, and the speed of sound in the gas that passes through the calibration the converter has passed through. To the output voltage to use it for a display of the relative speed of sound, more circuitry is required because the output signal) of amplifier 156 for use as an error signal is provided to the frequency of the voltage controlled To set the oscillator VCO, and as an input signal for the circuit of FIG. 6.

Another design enables the output voltage to be set equal to the value Λ if, for example, air is present in the converter arrangement. If the speed of sound of the gas flowing through the transducer arrangement changes, the magnitude of the output voltage corresponds to the speed in the gas relative to the speed in air.

809838/0601

The circuit of Fig. 6 includes circuitry for accepting the uncorrected flow rate from the output of amplifier 150 in S ¹ Xg. 5 and generates an output signal indicating the corrected flow rate. The output of "amplifier 150" has been found to have an error proportional to ty, / £ 2 »where f ^ is the initial trim frequency of the voltage controlled oscillator in FIG The circuit of Fig. 6 multiplies the uncorrected flow rate output of amplifier 150 by fp / f ^ j to produce a corrected flow rate signal at terminal 7 of amplifier LK324- B in FIG. 6.

The error voltage of the voltage-controlled oscillator, which appears at the output of the amplifier 156 in FIG. 5, is proportional to the frequency and is used to generate a correction factor for correcting the flow velocity. The operational amplifier LM3O8 ^ .er 3? Is x 6 acts as a signal fornier, and receives the error voltage (0D + 0Ü) of the voltage controlled oscillator. By setting the resistor connected to amplifier LM3O8 for adjustment to 0 xtf, an output voltage of 0 volts is generated at connection 6 if the fault voltage has the nominal level of +7.5 volts. Ore the signal conditioner EUGT an output voltage of +.1,05 volts per deviation from - 5KBz.

The output signal at connection 6 of the amplifier I1M3O8 then modulates a duty cycle modulator made up of amplifiers LH324-A and LM3II and those connected to them

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Circuit is formed. If "the voltage controlled Oscillator works at the adjustment frequency, the output signal at the amplifier IM308 is equal to 0 and the Setting resistor for the application cycle that starts with the Amplifier LM324A is connected, is set to 50%, the field effect transistor switches Q14 and Q15 blocked for 50% of the time and conductive for 50% of the time are. As a result, the gain of the amplifier is LM324-B. 1 and there is no correction for the uncorrected Flow introduced from amplifier 150 in Fig. 5, • and the output signal at connection 7 of the amplifier LM324B indicates the flow rate of the gas through the converter.

When the operating frequency of the voltage-controlled oscillator changes, a voltage appears at terminal 6 of the Amplifier LM3O8 in Fig. 6 positive for a drop of frequency and negative for an increase in frequency. This voltage modulates the duty cycle generator, which changes the cycle of use. The change in the duty cycle causes a change in the gain of the Amplifier LM324B depending on a change in Frequency of the voltage controlled oscillator so that the The uncorrected flow rate signal of Fig. 5 is changed by amplifier LM324B so that the output signal is proportional to the flow rate through the converter is.

The above description of an acoustic flow meter has placed particular emphasis on a preferred one electronic circuit that cooperates with a converter arrangement to not only control the gas flow and direction, but also to effect a measurement of the relative speed of sound in the flowing gas.

£ 09838/0601

2B07397

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The description has also, somewhat emphasized the fact that the invention for a flow meter is suitable with the -the direction of flow, the flow and the speed Schallge is to be measured in a gas, but the device is also used in the same way for measuring the direction of flow, the flow and the speed of sound in liquids, although then some circuit elements may require a change in their values in order to ensure the effectiveness of the flow meter for others Optimizing applications where the flow direction, flow and speed of sound in a gas are not should be measured. In addition, those skilled in the art will immediately recognize that other modifications to the flow meter are possible are without, however, the general idea of the invention and leave the scope of protection specified in the claims will. For example, instead of the phase detector and the phase sum and difference calculator, another equivalent Device used to calculate a quantity that is proportional to or equal to the speed of the acoustic Pressures in the converter are those of the sending migrate to the receiving transducer. Every calculated speed has two components, one of which is the The velocity of the flow fluid and the other the velocity of the acoustic pressures in the fluid are without fluid flow. One of these equivalent speed calculators can provide a facility for Bastimmen the time difference between the start of the acoustic Press on a sending transducer and the point in time at which the receiving transducer sends a received signal as a function of generated by the acoustic pressures. Each calculated time difference is also proportional to the speed the acoustic pressures traveling from the sending to the receiving transducer.

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Further advantages of the flow measuring device described can be obtained by combining or rearranging the signals indicating the various parameters. So cause Z..B. Changes in the gas composition that cause a change in the molecular weight of the gas mixture, including a change in the speed of sound. In this way, a transition from a gas mixture A with an average molecular weight M ^ to a gas mixture B with an average molecular weight M _ß and the proportion of the gas mixture A mixed with the gas mixture B can be measured. Such a technique can be performed with a gas flow meter B. can be used to provide a proportional measurement of the proportion of carbon dioxide in the exhaled breath compared to that in the inhaled mixture.

Since the speed of sound is given by:

c = v ^ - meter / sec

is, where

y = the ratio of the specific heat at constant Pressure to that at constant volume,

k = Boltzmann's constant of 1.38 χ 10 "^ Joule / ° C, T = the absolute temperature ⁰ C and
M = the mass of the molecules in the gas in kg are, it is seen that the molecular weight is proportional to c ~~ 'and 3 ^l Achmann will immediately recognize that an electrical output signal can be generated, which is proportional to changes in molecular weight , while the other variables remain constant It is clear that this simple case can be extended to include changes in specific heats and temperatures with changes in molecular weight, so that gas mixture A is defined by a group of conditions and gas mixture 3 is defined by a group of conditions another group of conditions can be specified.

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In addition, if the pressure or density changes greatly, the volumetric flow can be corrected to approximately standard conditions or the actual Hassen flow by combining a pressure measurement with parameters obtained from the flow meter described are. The mass flow is given by

M = V mp / kü) Eilograms / sec

where ρ = the pressure in ITewtons / meter ¹ ".

The above equation for the speed of sound c then results

H = 7 ρ y / c ² .

It will be immediately apparent to those skilled in the art that a pressure transducer can be used to measure the absolute pressure in the flow meter. In addition, the output signal of the pressure transducer is multiplied by the volumetric flow Y from the flow meter and divided by the square of the speed of sound c, so that a signal from the flow meter together with suitable constants can also give an approximate value for the actual mass flow.

While a constant value for f gives an error in the value for some changes in gas mixture, there are many cases where changes in the value of γ are insignificant. The use of the parameters described above to generate a signal for the volumetric flow reduced to a standard temperature and pressure is also obvious to the person skilled in the art.

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Having a flow meter system for accurately measuring flow rate regardless of composition as has been described, it is clear that this technique can also be used to advantage in other acoustic flow meters can be used in which the hoof formers are not cylindrical or arched, but in the Are flow path or form certain obstacles or recesses along the flow path. This means, every acoustic flow meter can extract parts of the gate from this technology if errors are caused by changes in the Speed of sound in the fluid are conditioned.

The person skilled in the art recognizes that the acoustic flow measuring device described above fulfills the principle aim of the invention, i.e. the accuracy of the flow meter is relatively independent of changes in gas composition. Those skilled in the art will also recognize that the above and other changes have been made in the circuit described can be used to achieve equivalent effects, without departing from the general inventive concept as indicated in the claims.

$ 09838/0601

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ersei \ e

Claims (1)

PATENT ADVOCATES A. GRÜNECKER D1PL.-ING. H. KINKELDEY OR-INa 2807397 W. STOCKMAlR DR-INa ■ AeclCALTEO « K. SCHUMANN OR RER NAT - OPL-PHYS P. H. JAKOB DIPU-ING. P 12 406 G. BEZOLD DR RER NAX- OiPL-OSVl 8 MUNICH MAXIMILIANSTRASSE Claims 1.) A flow measuring device for a fluid flowing along a path, characterized by the combination of a device (14, 28) for determining a path including the flow of fluid along the path arranged first and second transducers (24, 25), one with the first and second Transducer connected transducer control circuit (50) so that the first transducer (24) generates first acoustic pressures in the fluid and the second transducer (26) generates a first received signal when the first acoustic pressures are detected by it during a first transmit-receive cycle v / ground, and thus the second transducer (26) generates second acoustic pressures in the fluid and the first transducer (24) generates a second received signal when the second acoustic pressures are sensed by it during a second transmit-receive cycle, wherein the converter control circuit (50) a switch device (Qc ₅ Q / -) for switching over from the first to the second transceiver ngs cycle, a first measuring device (58) for measuring a first phase difference which is the phase difference between the first acoustic pressures, 809838/0801 TELEPHONE (OSB) 23 28 βθ TELEX O5-S9 38O T = LEQRAMME. MONAPAT TELECOPER generated by the first transducer (24), and the first received signal generated by the second transducer (26) during each first transmit-receive cycle to v / eist, a second measuring device (58) for measuring a second phase difference comprising the phase difference between the second acoustic pressures generated at the second transducer (26) and the second received signal generated by the first transducer (24-) during every second transmit-receive cycle a differential device (66) responsive to the first and second measuring devices (58) for generating a difference, the magnitude of which is equal to the difference between one of the first phase difference and one of the second phase difference, the magnitude of the difference signal being directly related to the instantaneous flow mean flow rate and the "sign of the difference signal indicates the direction of fluid flow along the path, and one with the umf ormer control circuit (50) connected device (YCO) _? for automatically adjusting the frequency of the acoustic pressures generated by each of the transducers (24,26) to a frequency at which a resonance echo occurs across the diameter of one of the transducers (24,26) in order to maximize the size of the received signal, generated at the other transducer so that the differential output of the flow meter is independent of the speed of sound in the fluid. 2. Flow meter according to claim 1, characterized in that the first and second transducers (24,26) each have a sending and a separate receiving transducer. 809838/0601 2807237 3. Flow meter according to claim 1 or 2, characterized by means for displaying the Sum of the first phase difference and the second phase difference, the size of the displayed sum being based on relates to the speed of sound in the fluid. 4. Flow meter according to one of claims 1 to 3> characterized in that each converter (24, 26) has a cylindrical body, the inner lateral surface of which is essentially in alignment with the device (14,28) is designed to determine the path including the fluid flow, so that the converters (24,26) do not impede the flow of fluid. 5- flow meter according to claim 4, characterized in that ge k e η η that each converter (24,26) has a crystal. 6. Flow meter according to claim 5i, characterized in that the crystal material is a material from polyvinyl fluorides, barium titanate, lead zirconate titanate, Quartz, tourmaline, high polymer organic piezoelectric Materials or group comprising polarized polycrystalline ferroelectric ceramic materials ha u - 7 flow measuring device according to one of claims 1 to 6, characterized in that the device (VCO) for automatically setting the frequency of the acoustic pressures has an oscillator for generating a signal at a frequency that is at least partially is determined by the sum of the first phase difference and the second phase difference. 809838/0601 2807337 8. flow meter according to one of claims 1 to 7? characterized in that the converter control circuit (50) additionally has a device (Q ^ to for continuous switching between the first send-receive cycle and the second transmit-receive cycle. 9- flow measuring device according to one of claims 1 to 8, characterized in that means (146, 14-8) for storing the first phase difference and the second phase difference is provided. 10. Flow meter according to one of claims 1 to 9? characterized by a device (Pig.6) responding to the difference signal for correcting the Difference signal into a corrected flow velocity signal. 11. Flow meter according to one of claims 1 to 10, characterized by acoustic damping material (30,32), which is arranged along the path at a point, in order to detect the acoustic pressures of one of the Converter (24-, 26) against leaving the facility (14.28) to determine the path to be reduced significantly, and to substantially reduce reflected acoustic pressures compared to penetration into the device (14-, 28) sum determining the way. 12. Flow meter for a fluid flowing along a path, characterized by the Combination of a tubular body (14-) for defining a path including the fluid, an adjustable one Oscillator (VCO) for generating a signal at an adjustable frequency, a switch device (ijy, to Q, -) to switch the signal alternately into an upstream and a downstream signal, 809838/0601 a first converter device (24-) and a second Converter means (26) which are arranged at a distance from one another along the tubular body (14-), wherein the first converter device (24-) to the upstream signal and the second converter device (25) to the responding downstream signal, the first transducer means (24 ·) upstream acoustic pressures in the Fluid generated as a function of the upstream signal and the second converter device (26) is responsive to the upstream acoustic pressures by generating an upstream received signal, the second transducer means (26) downstream acoustic pressures in the fluid due to the downstream Signal generated and the first converter device (24 ·) is responsive to the downstream acoustic pressures by generating a downstream received signal, one Phase detector (58) that responds to any upstream signal and responsive to each upstream received signal to produce an upstream nose difference that is the Has phase difference between the upstream signal and the upstream received signal, the Bevel detector (58) is also responsive to any downstream signal and any downstream received signal, to generate a downstream phase difference which is the phase difference between the downstream signal and the downstream received signal comprises means (66) for generating the sum of an upstream Phase difference and a downstream nose difference and a device (15 ^ ·, 156) that acts on the Sum of an upstream phase difference and a downstream phase difference responds to the prequai ζ set the adjustable oscillator (VCO) to a frequency, in which a sesonance echo occurs across the diameter of one of the uniforms (24-, 26) when it hits a Signal responds. 809838/0601 13 · Flow measuring device according to claim 12, characterized by means (66) for generating the difference between the upstream phase difference and the upstream phase difference and by means for displaying the difference between the upstream phase difference and the downstream one Phase difference, the sign of this difference, which indicates the direction of fluid flow in the tubular body (14) and the magnitude of the phase difference which affects the velocity of the fluid flow relates. . Flow measuring device according to claim 12 or 13, characterized in that the first and the second Transformers (24, 26) each have a cylindrical body, the inner lateral surface of which corresponds to the inner lateral surface of the tubular body (14) is aligned. 15- flow meter according to one of claims 12 to 14, characterized by means for displaying the sum of the upstream phase difference and the downstream phase difference, the displayed sum of the speed of sound in the fluid is proportional. 16. Flow meter according to claim 12, characterized in that the first and the second Transducers (24,26) each have a transmitting and a separate receiving transducer. 17 · Flow measuring device according to one of claims 13 to 16, characterized by a device (150), the device setting the frequency ("VOO) and 809838/0601 responsive to the device (66) generating the difference, to generate a flow rate output signal, which indicates the flow rate of the fluid in the tubular body (14 *). 18. Flow meter for a fluid flowing along a path, characterized by the Combination of means (14,28) for determining a substantially enclosing fluid flow cylindrical path, through a first and a second substantially cylindrical converter (24,26), the longitudinal of the path, each transducer (24,26) having an inner diameter (D) which is substantially identical to the diameter of the path, a device (38,40) operatively coupled to each converter (24,26) for Feeding the first transducer (24) for generating first acoustic pressures at an adjustable frequency in the fluid and for generating first received signals at the second transducer (26) in response to the first acoustic press during a first send / receive cycle and for feeding the second transducer (26) to generate second acoustic pressures at the adjustable one Frequency in the fluid and for generating second received signals at the first transducer (24) as a function of the second acoustic pressures during a second transmit-receive cycle, a detector device (58) to determine a first speed specification during the first transmit-receive cycle, which is the speed of the acoustic pressures traveling from the first transducer (24) to the second transducer ^ has, and for determining a second speed s specification during the second send-receive cycle, 809838/0601 dle has the speed of the acoustic pressures that from the second converter (26) to the first converter (24) running, means (66) for summing the first and second speed data and one on these Sum of the first and second speed data responsive device (“VOC) for setting the frequency the - \ generated by the first or the second converter (24,26) acoustic pressures on the natural cavity resonance frequency the 02-testicle, the occurrence of a resonance echo over the diameter D of each of the Transformer (24,26) causes. 19 · Flow measuring device according to claim 18, characterized in that it is identified indicates that each converter (24,26) made of a material in the polyvinyl fluoride, barium titanate, Lead zirconate titanate, quartz, tourmaline, high polymer organic piezoelectric materials or polarized polycrystalline ferroelectric ^ ceramic Materials having group is produced. 20. Flow meter according to claim 18 or 19 ■> characterized in that the device (38,40) connected to each of the transducers (24,26) has a voltage-controlled oscillator (VCO), the frequency of which is partly dependent on the sum of the first phase difference and the second phase difference is controlled. 21. Flow meter according to one of claims 18 to 20, characterized by a device for displaying the sum of the first and second speed information, where the displayed sum relates to the speed of sound in the fluid in the path relates. 809838/0601 22. Flow meter according to one of claims 18 to 21, characterized by a device (66) for calculating the difference between the first speed specification and the second speed specification and by a device (J ¹ Ig-O) for correcting this difference for changes in the speed of sound in the fluid. 23 · Flow measuring device according to claim 22, characterized by a calculated on the corrected Difference and the frequency setting device (VCO) responsive device for generating the speed of sound signal indicative of the fluid in the path. 24. Flow meter for a flowing along a path Fluid characterized by the Combination of means (14,28) for determining a essentially enclosing the fluid flow cylindrical path, a first and a second, substantially cylindrical converter (24,26) extending along the Path are arranged, each converter (24,26) having an inner diameter (D) which is substantially identical to au the diameter of the path is, a device (Fig.2) to alternately generate a signal that a first Represents the send-receive cycle, and a signal that represents a second transmit-receive cycle, one operatively associated with each of the transducers (24,26) Means (38,40) for driving a signal to the first transducer (24) for generating first acoustic pressures in the Fluid and for receiving first received signals from the second transducer (26) resulting therefrom of the first acoustic pressures generated during the first transmit ... receive cycle, and for driving one 809838/0601 Signal to the second transducer (26) for generating and sum receiving second acoustic pressures in the fluid second received signals from the first converter (24-), generated by the latter as a function of the second acoustic pressures during the second transmit-receive cycle means (66) responsive to each first transducer driver signal and each first received signal to generate a first 3 proportional indication of the speed of the acoustic pressures from the first to the second transducers run, this facility responding to every second transducer drive signal and every second received Signal responds to produce a second proportional indication of the speed of the acoustic pressures that run from the second to the first converter, and each of the proportional values of the speed a! puncture of the Velocity of the acoustic pressures in the fluid as well as the sighting and velocity of the fluid along the path is a means of generating the sum of every first proportional indication and every second proportional indication, with each sum based on the current Speed of sound in the fluid flowing along the path is directly related, and one device (VCO) for controlling which is responsive to every sum the frequency of the acoustic pressures generated by both transducers (24 ·, 26) so that the distance (D) is perpendicular to the direction of fluid flow through the path is an eigenvalue number of the wavelengths, whereby a the natural frequency corresponding to the fluid flowing through is generated. 25 · Flow measuring device according to claim 24, characterized by a device for displaying each Sum, where the displayed sum equals the switching speed is in the fluid. 809838/0601 26. Flow meter according to claim 24 or 25, characterized by a device for Generate the difference between the first and the second proportional information, with the sign of the difference corresponds to the direction of flow along the path, and the magnitude to the velocity of the fluid flow is related. 27 · Flow measuring device according to one of Claims 24 to 26, characterized by a device to display each sum, where the displayed sum is based on the current speed in the flow * medium in the path is directly related. 28. Flow measuring device according to one of claims 24 to 27, characterized in that each converter (24 ·, 26) is made of a material in which polyvinyl fluorides, Barium titanate, lead zirconate titanate, quartz, tourmaline, high polymer organic piezoelectric materials or polarized polycrystalline ferroelectric group comprising ... ceramic materials. 29. Flow measuring device according to one of claims 24 to 28, characterized in that the device which is operatively coupled to each converter (24 ·, 26) (38,4-0) has a voltage-controlled oscillator (VCO), which is connected to the first and second converter (24-, 26) in each case during the first and the second send-receive cycle is coupled to generate the acoustic pressures, xiobei the frequency of the voltage controlled oscillator (VCO) is partly controlled by the sum. 30. Flow meter according to one of claims 18 to 28, characterized in that the frequency is held at such a value that D is substantially 809838/0601 equals 2,3 ^, where A is the wavelength of the Converters (24,26) in the fluid within the Generated sound is. 809838/0601